1. Field of the Invention
In general, this invention relates to removable pressure sensitive adhesives and articles made therewith. This invention further relates to removable pressure sensitive adhesives and articles that have excellent shear strength, demonstrate reduced adhesive transfer to a substrate, and are solvent resistant.
2. Description of the Related Art
Inherently tacky, elastomeric microspheres are known to be useful in repositionable pressure sensitive adhesives. Numerous references describe the preparation and/or use of solid, inherently tacky repositionable or reusable microsphere-based adhesives. Ideally, these adhesives can be repeatedly adhered to and removed from a substrate without substantial loss of adhesion capacity. See, for example, U.S. Pat. Nos. 3,691,140 (Silver); 4,166,152 (Baker et al.); 4,495,318 (Howard); 4,598,112 (Howard); and 4,786,696 (Bohnel). Reportedly, "the primary problem associated with these types of adhesives have been microsphere loss, i.e., microsphere transfer to the substrate." (See, for example, U.S. Pat. No. 4,994,322 (Delgado et al.))
There have been prior attempts to solve the problem of "microsphere loss." The typical approaches have been to use a binder, a primer, an adhesion promoting monomer, or other materials that reduce adhesive transfer. U.S. Pat. No. 3,857,731, (Merrill et al.); EPA 0209337 (Thomson et al.); DE 3,544,882 Al (Nichiban); U.S. Pat. No. 4,656,218 (Kinoshita); U.S. Pat. No. 4,645,783 (Kinoshita); and U.S. Pat. No. 5,118,750 (Silver et al.) are representative of these approaches.
Other attempts to attack the problem of microsphere transfer focus on the use of hollow, inherently tacky microspheres as described in U.S. Pat. Nos. 4,988,567 (Delgado) and 5,045,569 (Delgado). Hollow microspheres have also been combined with binders to further reduce adhesive transfer. See, for example, U.S. Pat. No. 4,994,322 (Delgado et al.).
However, a need still exists for removable pressure-sensitive adhesives that demonstrate reduced adhesive transfer without the use of binders.
Many of the foregoing patents describe the resulting microspheres as solvent insoluble and solvent dispersible. See, for example, U.S. Pat. Nos. 3,691,140 (Silver); 4,166,152 (Baker et al.); 4,786,696 (Bohnel); 4,988,567 (Delgado); 4,994,322 (Delgado et al.); 5,045,569 (Delgado); and 5,118,750 (Silver et al.). The microspheres do not dissolve in solvent but will disperse in the solvent. Consequently, an article prepared from these adhesives, such as a tape, could be susceptible to solvent attack since the microspheres would disperse in the solvent. There are many applications for which a removable pressure sensitive adhesive would benefit from also being solvent resistant, such as spray painting operations and bonding to oily substrates. There is especially a need for removable pressure sensitive adhesives that are resistant to non-polar organic solvents.